program triangle;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
  x1, y1, x2, y2, x3, y3, S1, S2, S3, xa, ya, Sa, Sx2:integer;

begin
  readln(x1, y1, x2, y2, x3, y3);
  if (x1>x2) and (x2>x3) then
    xa:=x1-x3;
  if (x2>x1) and (x1>x3) then
    xa:= x2-x3;
  if (x2>x3) and (x3>x1) then
    xa:= x2-x1;
  if (x3>x2) and (x2>x1) then
    xa:= x3- x1;
  if (x3>x1) and (x1>x2) then
    xa:= x3-x2
  else
    xa:=x3-x1;
  if(y1>y2) and (y2>y3) then
    ya:=y1-y3;
  if (y2>y1)  and (y1>y3) then
    ya:=y2-y3;
  if (y2>y3) and (y3>y1)then
    ya:=y2-y1;
  if (y3>y2) and (y2>y1) then
    ya:=y3-y1;
  if (y3>y1) and (y1>y2) then
    ya:=y3-y2
  else
    ya:=y3-y1;
  Sa:=xa*ya;
  S1:=abs((x1-x2)*(y1-y2)) div 2;
  S2:=abs((x2-x3)*(y2-y3)) div 2;
  S3:=abs((x3-x1)*(y3-y1)) div 2;
  Sx2:= 2*(Sa-S1-S2-S3);
  writeln(Sx2);
  readln;
end.
